The structure and function of myoepithelial cells in salivary glands

Abstract

Histochemical studies of myoepithelial cells were undertaken in order to provide further information about the structure and function of these cells in their normal environment in salivary glands and as an aid in their identification in abnormal situations such as in salivary gland tumours. In their normal environment they are eosinophilic, birefringent structures which lie deep to the basement membranes of the secretory acini and smaller ducts and may appear fusiform or spider-like, depending on the plane of section. They stain intensely with phosphotungstic acid haematoxylin and iron haematoxylin. In rat salivary glands alkaline phosphatase and adenosine triphosphatase are readily localized in the myoepithelial cells and NAD diaphorase and malic dehydrogenase can, with difficulty, be localized in them. However, the oxidative enzymes, acid phosphatase and non-specific esterase are present in high concentration in the epithelium of the acini and ducts so that their localization in myoepithelial cells at the optical microscope level is extremely difficult. Tyrosine and phospholipid are present in the myoepithelial cells but repeated attempts failed to demonstrate the presence of glycogen. It is generally considered that myoepithelial cells are contractile in nature and although they bear some histological and histochemical resemblance to smooth muscle, there are sufficient differences to indicate that they are not identical and that their metabolic processes differ. They may be best identified in an abnormal environment by the application of histochemical methods for tyrosine, alkaline phosphatase and adenosine triphosphatase.